[Lowfer] Audio Noise Floor Measurements on my TS450S

[Garry]

Andy,

I started listening for LF and VLF signals a few years ago with an Icom 
IC706MkIIG. It was also "deaf" below 1 MHz, probably a common situation 
with synthesized radios. I solved the limitation by using a lot of 
preamp gain ahead of the radio. You can tell if you have enough by how 
well the big military stations like NAA on 24 kHz, NLK on 24.8 kHz, and 
NML4 on 25.2 kHz come through. Perhaps a better solution is to mix the 
near-zero spectrum up to a frequency where the radio has good 
sensitivity. Mike, WA3TTS and others do this. The ready, inexpensive 
availability of 10 MHz OCXOs makes this approach attractive. It works 
without the need for preamps because the external noise at VLF is 
substantially greater than the 7 dB or so noise figure of the typical 
double-balanced mixer. Thus the mixer insertion loss isn't really 
noticeable.
-- 
Garry, K3SIW, EN52ta, Elgin, IL